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How to use Mosquito Bits on potted plants?

Christy Garrett

6 years ago

Two of my indoor plants seem to be infested with fungus gnats, and multiple sources recommended Mosquito Bits (Bti). However, the instructions say one teaspoon for 25 square feet, which seem to be for use outside. Both plants are in 8 inch pots and I'm not sure how much to apply to each. Google hasn't really turned up anything. Thanks!

Comments (4)

albert_135 　 39.17°N 119.76°W 4695ft.
6 years ago
Deep down in this detailed ''fact sheet'' I found : Fungus Gnats as Houseplant and Indoor Pests - 5.584 - ExtensionExtension - Larvae may be killed by the microbial insecticide Bacillus thuringiensissubsp. israelensis (Bti) when applied as a drench to the growing medium. However, formulations of Bti sold for fungus gnat control generally are unavailable through retail outlets.

There are quit a few other options discussed.
rhizo_1 (North AL) zone 7
6 years ago
Christy, your product is to be applied to the surface of water, not soil. I would fill a container with as much water as you will need to apply to your plants at the next watering day and sprinkle in a very small amount of the bits. Let it sit for awhile, stir it up, and water your plants.

If you read your label, you will see that it is intended to be used for containerized bodies of water where mosquitoes breed. It does happen to be effective for fungus gnat control, too, but need to be delivered to the potting soil via the watering can.

Don't make any more than you will need for one watering cycle, but you will have to use it one two or three watering days. Don't water more often than usual.

Albert, people have been using mosquito dunks and bits for a very, very, very long time as a method of biological control of fungus gnats for indoor plants. That, and changing the potting mix and watering habits can all work collectively to eliminate the problem.
Christy Garrett thanked rhizo_1 (North AL) zone 7
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Heavy infestations of fungus gnat larvae can truly cause problems for containerized plants. They feed on the tender roots. Bt is eaten by the LARVAE, not the gnats. The larvae subsequently develop a diseased (by the bacterium) intestinal system and die. No larvae means no adults flitting around laying eggs and annoying you. I've not used the pelletized Bt, but don't see why it couldn't be used the same way as the round mosquito dunks. Put a small amount in your watering containers and allow to soak over night in water. Use THAT water on watering day for the next several times that you water. Don't water more than you usually would. As far as the bird bath goes, it can be simply rinsed out every other day or so and no mosquito niaids will have time to emerge as adults. Warning labels like that are on just about anything you use. Look at your shampoo bottle. If the labels were not present, and someone took it upon himself to drink or eat something not intended for drinking or eating, then the lawsuits would be never ending. Besides, just because a product is considered 'safe' and 'natural', does NOT mean that doesn't have hazards when used improperly. You should consider the underlying cause of the fungus gnat infestation at some point in the future. Switching to a coarse, fast draining potting medium will be a huge step in halting further problems without Bt, as will making sure you aren't watering excessively.
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Christy Garrett
Original Author
6 years ago
Thanks for the tip. How much is a "very small amount"? And yeah, the mistake I made was topdressing with moss. I thought it would help increase humidity, but it just made the problem worse. I amended it!
raleigh01
5 years ago
How much did you end up using for your 8 inch potted plants?

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